Homologous recombination is the process by which two chromosomes, paired up during prophase 1 of meiosis, exchange some distal portion of their DNA.

Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but to the different end piece.

If they break at the same place or locus in the sequence of base pairs, the result is an exchange of genes, called genetic recombination.

This outcome is the normal way for crossover to occur.

If they break at slightly different loci, the result can be a duplication of genes on one chromosome and a deletion of these on the other.

This is known as an unequal crossover.

If chromosomes break on both sides of the same centromere and rejoin to exclude the centromere, the result can be one chromosome being lost during cell division..

For more information about the topic Chromosomal crossover, read the full article at Wikipedia.org, or see the following related articles:

Genetic recombination — Genetic recombination is the transmission-genetic process by which the combinations of alleles observed at different loci in two parental individuals ...  > read more

Meiosis — In biology, meiosis is the process by which one diploid eukaryotic cell divides to generate four haploid cells often called gametes. Meiosis is ...  > read more

Trait (biology) — In biology, a trait or character is a feature of an organism. The term phenotype is sometimes used as a synonym for trait in common use, but strictly ...  > read more

Allele — An allele is a viable DNA (deoxyribonucleic acid) coding that occupies a given locus (position) on a chromosome. Usually alleles are sequences that ...  > read more

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